Fix gh 1241

dpctl/tensor/_dlpack.pyx

@@ -32,7 +32,7 @@ from .._backend cimport (
     DPCTLSyclDeviceRef,
     DPCTLSyclUSMRef,
 )
-from ._usmarray cimport usm_ndarray
+from ._usmarray cimport USM_ARRAY_C_CONTIGUOUS, usm_ndarray
 
 from platform import system as sys_platform
 
@@ -158,9 +158,11 @@ cpdef to_dlpack_capsule(usm_ndarray usm_ary):
     cdef int64_t *shape_strides_ptr = NULL
     cdef int i = 0
     cdef int device_id = -1
+    cdef int flags = 0
     cdef char *base_ptr = NULL
     cdef Py_ssize_t element_offset = 0
     cdef Py_ssize_t byte_offset = 0
+    cdef Py_ssize_t si = 1
 
     ary_base = usm_ary.get_base()
     ary_sycl_queue = usm_ary.get_sycl_queue()
@@ -223,9 +225,17 @@ cpdef to_dlpack_capsule(usm_ndarray usm_ary):
     for i in range(nd):
         shape_strides_ptr[i] = shape_ptr[i]
     strides_ptr = usm_ary.get_strides()
+    flags = usm_ary.flags_
     if strides_ptr:
         for i in range(nd):
             shape_strides_ptr[nd + i] = strides_ptr[i]
+    else:
+        if not (flags & USM_ARRAY_C_CONTIGUOUS):
+            si = 1
+            for i in range(0, nd):
+                shape_strides_ptr[nd + i] = si
+                si = si * shape_ptr[i]
+            strides_ptr = <Py_ssize_t *>&shape_strides_ptr[nd]
 
     ary_dt = usm_ary.dtype
     ary_dtk = ary_dt.kind

dpctl/tests/test_usm_ndarray_dlpack.py

@@ -178,3 +178,18 @@ def __dlpack__(self):
 
     with pytest.raises(TypeError):
         dpt.from_dlpack(DummyWithMethod())
+
+
+def test_from_dlpack_fortran_contig_array_roundtripping():
+    """Based on examples from issue gh-1241"""
+    n0, n1 = 3, 5
+    try:
+        ar1d = dpt.arange(n0 * n1, dtype="i4")
+    except dpctl.SyclDeviceCreationError:
+        pytest.skip("No default device available")
+    ar2d_c = dpt.reshape(ar1d, (n0, n1), order="C")
+    ar2d_f = dpt.asarray(ar2d_c, order="F")
+    ar2d_r = dpt.from_dlpack(ar2d_f)
+
+    assert dpt.all(dpt.equal(ar2d_f, ar2d_r))
+    assert dpt.all(dpt.equal(ar2d_c, ar2d_r))